title: Bcl-XL cooperatively associates with the Bap31 complex in the endoplasmic reticulum, dependent on procaspase-8 and Ced-4 adaptor.
abstract: Bap31 is a polytopic integral membrane protein of the endoplasmic reticulum and forms a complex with Bcl-2/Bcl-XL and procaspase-8 (Ng, F. W. H., Nguyen, M., Kwan, T., Branton, P. E., Nicholson, W. D., Cromlish, J. A., and Shore, G. C. (1997) J. Cell Biol. 139, 327-338). In co-transfected human cells, procaspase-8 is capable of interacting with Ced-4, an important adaptor molecule in Caenorhabditis elegans that binds to and activates the C. elegans procaspase, proCed-3. Here, we show that the predicted death effector homology domain within the cytosolic region of Bap31 interacts with Ced-4 and contributes to recruitment of procaspase-8. Bcl-XL, which binds directly but weakly to the polytopic transmembrane region of Bap31, indirectly and cooperatively associates with the Bap31 cytosolic domain, dependent on the presence of procaspase-8 and Ced-4. Ced-4Deltac does not interact with Bcl-XL but rather displaces it from Bap31, suggesting that an endogenous Ced-4-like adaptor is a normal constituent of the Bap31 complex and is required for stable association of Bcl-XL with Bap31 in vivo. These findings indicate that Bap31 is capable of recruiting essential components of a core death regulatory machinery.
authors.affiliation: Department of Biochemistry, McGill University, Montreal, Quebec H3G 1Y6, Canada.
authors.forename: F W
authors.initials: FW
authors.lastname: Ng
authors.forename: G C
authors.initials: GC
authors.lastname: Shore
mesh_terms: D029742:Caenorhabditis elegans Proteins; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D004792:Enzyme Precursors / Q000378:metabolism*; D015801:Helminth Proteins / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins; D011485:Protein Binding; D011506:Proteins / Q000378:metabolism*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D051020:bcl-X Protein
chemical_list: C091247:BCAP31 protein, human; C494811:BCL2L1 protein, human; D029742:Caenorhabditis elegans Proteins; D002135:Calcium-Binding Proteins; C089224:Ced-4 protein, C elegans; D004792:Enzyme Precursors; D015801:Helminth Proteins; D008565:Membrane Proteins; D011506:Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D011994:Recombinant Proteins; D051020:bcl-X Protein; C505530:CASP8 protein, human; C506433:CASP9 protein, human; D053181:Caspase 8; D053453:Caspase 9; D020169:Caspases; D003546:Cysteine Endopeptidases